LONDON, PHILADELPHIA
& OXFORD, U.K.—Adaptimmune Therapeutics plc and GlaxoSmithKline plc have announced the expansion of their strategic collaboration agreement to
accelerate Adaptimmune's lead clinical cancer program, an affinity enhanced T-cell immunotherapy targeting NY-ESO-1, toward pivotal trials in synovial
sarcoma. The companies announced their agreement in June 2014 for up to five programs, including the lead NY-ESO TCR program. Per the agreement, GSK has an
option on the NY-ESO-1 program through clinical proof of concept and, should it choose to exercise that option, will assume full responsibility for the
program.

The terms of the expanded agreement stipulate that the companies will accelerate the development of
Adaptimmune’s NY-ESO therapy into pivotal studies in synovial sarcoma and will explore development in myxoid round cell liposarcoma. Additionally, GSK
and Adaptimmune may initiate up to eight proof-of-principle studies exploring combinations with other therapies, including checkpoint inhibitors. Per the
expanded development plan, Adaptimmune will conduct the studies with GSK effectively funding the pivotal studies and sharing the costs of the combination
studies via a success-based milestone structure.

“We are delighted to broaden our collaboration with GSK,
which is also fully committed to the development of this revolutionary T cell therapy,” James Noble, CEO of Adaptimmune, said in a press release.
“We believe that our affinity enhanced T cell programs have the potential to deliver important clinical benefit to cancer patients, and it is therefore
essential that we accelerate our efforts to meet their needs. We are working closely with GSK to expedite development of our affinity enhanced T cell therapy
targeting NY-ESO, and if we succeed in generating pivotal data consistent with that of our ongoing studies, we believe it has the potential to be the first
engineered T cell therapy to reach the market.”

Previous guidance relating to the collaboration disclosed
potential cash payments to Adaptimmune of approximately $350 million over the first seven years from 2014 in relation to NY-ESO and two further programs.
Given the changes announced today, and the advances made across the collaboration, Adaptimmune is updating and expanding this disclosure. Under the terms of
the expanded agreement, the potential development milestones Adaptimmune is eligible to receive solely in relation to the NY-ESO program could amount to
approximately $500 million, excluding previously received payments, if GSK exercises its option and successfully develops NY-ESO in more than one indication
and more than one Human Leukocyte Antigen type. In addition, Adaptimmune would receive tiered sales milestones and, as previously disclosed, mid-single to
low double-digit royalties on worldwide net sales. GSK has the right to nominate up to four additional targets in due course and Adaptimmune is eligible to
receive further significant undisclosed milestone payments in relation to these earlier stage target programs.

“At GSK, we’re progressing a pipeline of immuno-oncology therapies to stimulate anti-tumor immunity in patients. As we highlighted to
investors at our R&D event last year, this Adaptimmune collaboration is a key element of that pipeline and is part of a comprehensive program for cell
and gene therapy. With this expanded collaboration, we have the opportunity to accelerate the lead program in synovial sarcoma toward pivotal trials and also
to investigate several other tumor types and combine the T cell therapy with immune-modulating therapies such as checkpoint inhibitors,” Dr. Axel Hoos,
senior vice president of Oncology R&D at GSK, commented in a statement.

Adaptimmune has also reiterated its
prior cash burn guidance, which remains unchanged as the majority of the expansion and acceleration costs will be funded by GSK. For the full year 2016, the
company expects its cash burn to be between $80 million and $100 million, excluding cash burn associated with business development activities, and expects
its cash position at Dec. 31, 2016, including cash, cash equivalents, and short term deposits, to be at least $150 million.